Why does February have only 28 days?

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We can blame the Romans for the quirks of our modern calendar. The ancient Roman calendar had only 10 months, beginning in March and ending in December. The cold winter months weren’t counted – most likely because they weren’t important to the agricultural cycle of planting and harvest. The months were synchronized with the moon, so some had 29 days and others had 31.

Around 713 BC, King Numa Pompilius added January and February, giving the year a total of 355 days. The name February comes from the Latin word for “purification,” because a purification ritual honoring the dead was performed in that month. In order to keep the calendar properly aligned with the seasons, it was necessary to add a short extra month (called Intercalaris) after February every 2-3 years.

Julius Caesar reformed the calendar again in 45 BC, abandoning the lunar model and following the solar year of 365 days. Extra days were added to January, August, December, April, June, September, and November, but February stayed at 28. Every four years (including in 2012) an extra day is added to February to keep the year in sync with the sun. A year in which February has 29 days is called a “leap year.”